We see traffic control systems at many road intersections. In the United States, the acceptable traffic control system is a traffic light system for each intersection direction having a red, yellow and green indicator (light) The green indicates the traffic in that direction can proceed through the intersection. The yellow indicates that the traffic light is transitioning between green and red and traffic should prepare to stop. The red indicates the traffic in that direction should stop. In some systems, multiple sets of lights are configured in a given direction with some dedicated to traffic in turn lanes.
The traffic control system has timers that are programmed to control the duration of each signal depending upon the average traffic levels and the amount of time required to move across an intersection, etc. Some traffic control systems are coupled to one or more nearby traffic control systems to provide synchronization between multiple traffic control systems to aid in the efficient flow of traffic. Additionally, some traffic control systems are capable of being centrally controlled by an operator, whereby an operator is provided with tools to change timing, etc., to improve traffic flow.
During unusual traffic patterns such as when an event begins or is finished, often the traffic control system is manually operated by a police officer. In such, the police officer access the control box (unlocks and opens a door) of the traffic control system and switches the traffic control system from automatic to manual. From there, the police officer changes the state of the traffic control system by operating a manual control. When finished, the police officer switches the traffic control system back into automatic mode and closes/locks the traffic control system door. Unfortunately, there are circumstances where the police officer must leave in an emergency. In such, if the police officer forgets to switch the traffic control system back to automatic mode, the traffic control system will remain green in one direction and red in the other direction, causing a major traffic problem.
What is needed is a traffic control system that will revert to an automatic mode when left unattended in a manual mode.